1. Field of the Invention
The present invention relates to power device packages and methods of fabricating the power device packages, and more particularly, to power device packages which reduce the stress exerted on a power device die and a method of fabricating the power device packages.
2. Description of the Related Art
One type of conventional power device package has at least one semiconductor power device bonded directly to a lead frame and sealed with an molding resin such as an epoxy molding compound (EMC).
However, when the semiconductor die is directly bonded to the lead frame as in this type of conventional power device package, the semiconductor die is stressed by a temperature change since the coefficient of thermal expansion (CTE) of a semiconductor die is substantially different from that of a lead frame on which the semiconductor die is bonded. As such, the semiconductor die is deformed by the stress, and the performance of the semiconductor die usually deteriorates. Moreover, the stress exerted on the semiconductor die results in an inferior and deformed power device package. In addition, the deformed power device packages can crack and foreign substances such as water can penetrate into the power device package through the cracks.
FIG. 1 is a cross-sectional view illustrating a conventional power device package.
Referring to FIG. 1, a silicon power device die 30 is bonded to a lead frame 10 using a conductive adhesive material 20, and the lead frame 10 and the silicon power device die 30 are sealed with a sealant 40 such as an EMC. Conventionally, the lead frame 10 is formed of copper (Cu), and the CTE of the copper is 17 ppm/° C. However, the CTE of the silicon power device die 30 is 2-3 ppm/° C.
If the temperature of the conventional power device package increases due to heat generated during operation of the conventional power device package or applied to the conventional power device package from an outside heat source, the power device die 30 is stressed. The lead frame 10 expands more than the semiconductor die 30 and, as a result, the semiconductor die 30 can be deformed (strained).
In the conventional power device package illustrated in FIG. 1, the sealant 40 has a short surface creepage distance from the outside of the conventional power device package to the silicon power device die 30. Therefore, the sealant 40 can easily crack off from the lead frame 10 and the silicon power device die 30 due to the difference in the CTEs of the silicon power device die 30 and the lead frame 10. Foreign substances such as water can penetrate into the silicon power device die 30 through the cracks resulting in defective power device packages.
In addition, since the conventional power device package has the silicon power device die 30 directly bonded to the lead frame 10, the size of the silicon power device die 30 is limited to the size of the lead frame 10.